The proposed research projects involve light and electron microscopic studies of the developing and adult visual system. Development of the human retina will be studied in a sample of 72 fetal retinae previously fixed and embedded. Cat retinae of 1,2,10, and 18 days postnatal age will be examined by electron microscopy. Larvae of Xenopus laevis will be prepared for electron microscopy at different developmental stages to determine the developmental sequence of ultrastructural changes during photoreceptor synaptogenesis and outer segment formation. Certain stages of larvae will be labeled with H3 leucine and prepared for electron microscope autoradiography to study membrane formation at the earliest stages of outer segment development. Xenopus larvae eye explants will be grown in culture and examined for retinal differentiation by comparison to normal eyes. The photoreceptors of various species of arboreal and terrestrial squirrels will be examined by electron microscopy for purposes of describing ultrastructural features of rods and cones. Aspects of membrane disposal and formation will be studied by autoradiography. Acid phosphatase localization techniques will be used to study characteristics of dense granules in the ground squirrel pigment epithelium. The compressed optic projection will be studied in the goldfish optic tectum by electron microscopy and golgi impregnations. The visual system of the 4-eyed polychaete Nereis virens will be studied by electron microscopy.